International Journal of Applied Chemistry.

ISSN 0973-1792 Volume 13, Number 4 (2017) pp. 801-811

© Research India Publications

http://www.ripublication.com

Elemental Analysis of Rice Husk Using Proton-

Induced X-Ray Emission (Pixe) Spectrometry

Clementina D. Igwebike-Ossi

Department of Industrial Chemistry, Faculty of Science, Ebonyi State University, Abakaliki, Nigeria.

Abstract

Rice husks, an agro-waste is of increasing interest to researchers as

bioresource for domestic and industrial applications due to its abundance,

cheapness and ‘renewability’. In this study, the elemental composition of rice

husk was determined using the high-tech, highly sensitive and uncommon

Proton-induced X-ray emission (PIXE) spectrometry. Milled rice husks,

obtained from a rice mill in Abakaliki, Nigeria were first washed to remove

sand and stone contaminants and then dried in an oven. The clean husks were

ground to a fine powder, pressed into pellets and subjected to analysis using

the PIXE technique. The results of the analysis revealed the presence of a total

of thirteen elements. The elements detected and their concentrations (in %) are

: Si as SiO2 (25.82±0.024), Al (0.017±0.001), Fe ( 0.039± 0.001), Ca

(0.088±0.002), Mg (0.135± 0.02 ), Na (0.03±0.01), K (0.099±0.003), P

(0.666±0.023), S (0.217±0.009,), Cl (0.026±0.005), Ti (0.006±0.001), Mn

(0.012±0.001) and Zn (0.001±0.000).The results showed that the predominant

element in rice husks is silicon which occurs in the form of silica (SiO2) as it

was found to constitute 95% of the total elements present while the other

twelve elements made up only 5%. P was present in a small quantity; Al, Fe,

Ca, Mg, Na, S, K, Cl and Mn were in minute quantities while Ti and Zn were

in trace quantities.

Keywords: PIXE spectrometry, rice husk, silica, elemental composition,

analysis

802 Clementina D. Igwebike-Ossi

INTRODUCTION

Rice husks (or hulls), the hard, outer protective covering of the rice grain, are

generated in large quantities as agro-waste in the rice-producing areas of the world

during the milling of rough rice (paddy) to obtain white rice. The ongoing

revolutionary, global transition from the use of non-renewable to renewable resources

due to environmental protection consideration has stimulated several research

investigations into the use of rice husks as potential domestic and industrial bio-

resource. Thus, rice husks have been found to be useful in several applications which

include production of ethanol [1], lightweight bricks [2], particle board [3], as

adsorbent [4], fertilizer production [5], fuel for power generators, domestic stoves and

industrial furnaces [6, 7]. Rice husk is also a source of rice husk ash (RHA) which has

also been found suitable for several industrial applications. [8-11]. Rice husk

therefore presents a cheap, abundant and renewable resource which makes it attractive

to researchers for various studies.

Plants absorb and accumulate silica from the soil into their systems to varying levels;

0.1-15% of their dry weight [12]. Among them monocots, such as rice, Oryza sativa ,

wheat, maize and barley are categorized as Si-accumulators due to their high silica

contents (10-15%) [13]. Earlier investigations carried out to determine the chemical

nature of rice husks, revealed that it contains a high proportion of lignin and about

20% of their outer surfaces are covered with silica [14] The presence of silica in rice

husks was further confirmed by Bharadwaj et al [15] from the scanning electron

microscopic image of a virgin rice husk particle in which he observed that the

structure resembled that of a composite material with fibres composed of silica

regularly interspaced in the matrix. The matrix consisted largely of cellulose,

hemicelluloses and lignin which are thermo-chemically unstable and decompose on

heating.

The elemental components of rice husks constitute only a fraction of its chemical

composition and are often mentioned in relation with the lignocellulosic components,

which include lignin, hemicellulose and cellulose. Muntohar [16] gave the chemical

composition of rice husks as typically : cellulose (40-45%), lignin (25-30%), ash (15-

20%) and moisture (8-15%). In another study, [17] the composition of rice husks was

reported as 32.24% cellulose, 21.34% hemicelluloses, 21.44% lignin, 1.82%

extractives, 8.11% water and 15.05% mineral ash, which gives the total

lignocellulosic composition as 75.02%. Similarly, Daifullah et al [18] and Arnesto et al [19] presented the main constituents of rice husks as 64-74% volatile matter, 12-16

fixed carbon and 15-20% ash. However, in another study, the ash content of rice

husks from different species of rice was found to be in the range of 18-25% [20] while

in another report on the analysis of rice husk, Maeda et al [21], gave the ash content

as 22-29%. Silica, in rice husks is often referred to as ‘ash’ because it is the residue of

combustion of rice husks. The ash also contains other elemental components in small

Elemental Analysis of Rice Husk Using Proton-Induced X-Ray Emission (Pixe).. 803

quantities. The result of the analysis of a rice husk sample from India [22] showed the

elemental components (in mass fraction %) to be as follows: C (41.44), H (4.94), O

(37.32), N (1.1), Si (14.66), K(0.59), Na (0.035), S (0.300, P(0.07), Ca(0.06), Fe

(0.006) and Mg (0.003). Chockalingam et al [23] reported the presence of K, Mg,

Na, Ca, Mn, Fe, B, Cu, Zn, PO4 and NO3 in the elemental analysis of another rice

husk sample from India.

The most common types of analyses that have been carried out to determine the

chemical composition of rice husks are proximate analysis, [23, 24] ultimate analysis,

[23-25] and component analysis (lignocellulosic contents) [16]. Other methods that

have been employed involve the conversion of rice husks to rice husk ash (RHA) and

subsequent analysis of the RHA samples, using X-ray emission analytical techniques

such as X-ray fluorescence (XRF) [26, 27]. In the XRF analysis of RHA samples

obtained by burning rice husks from Benue and Kogi states of Nigeria thirteen

elements (in the form of their oxides) were detected : K, Ca, Cr, Mn, Fe, Ni, Cu, Zn,

Sr, Br, I, As, and Cl [27]. Igwebike-Ossi [28] reported the presence of fourteen

elements (in the form of their oxides) in RHA but with a preponderance of Si (present

as SiO2) using the PIXE technique. The elements reported were as follows ; SiO2

Al2O3 Fe2O3 CaO MgO Na2O, K2O, P2O5, SO3 ClO3, TiO2 MnO, ZnO and Rb2O.

Another technique that has been used for RHA compositional analysis is Atomic

Absorption Spectrometry (AAS) [29].

Proton-Induced X-ray emission or particle-induced X-ray emission (PIXE )

spectrometry is a powerful, non-destructive, analytical technique used to determine

the elemental composition of a solid, liquid, thin film and aerosol filter samples [30,

31]. It is based on the energy spectra of characteristic X-rays emitted by the de-

excitation of the atoms in the sample bombarded with high energy protons (1-3 MeV)

with the aid of a suitable energy dispersive detector [31]. PIXE can detect all

elements, from sodium to uranium, giving a total of seventy-two elements (excluding

Po, At, Fr, Ra, Ac, Pa and the inert gases [31].The use of proton beams as excitation

source in PIXE offers several advantages over other X-ray techniques, the major ones

being its high sensitivity for trace elements and lower atomic number elements

determination as well as its higher rate of data accumulation across the entire

spectrum which allows for faster analysis [31]. PIXE is capable of detecting elemental

concentrations down to parts per million, however, the technology is still relatively

new in wider avenues of chemical research. The greater sensitivity of PIXE is

expected to give more accurate results than other analytical techniques earlier

mentioned [27, 29].

The variation in the chemical composition of rice husks is due to its dependence on

several factors which include soil chemistry, climatic conditions, paddy variety

[32,33], use of fertilizer, type of fertilizer [34, 35], year of harvest, sample preparation

and methods of analyses [20].

804 Clementina D. Igwebike-Ossi

There is very limited information in literature on the use of the relatively new, high-

tech and highly sensitive Proton-induced X-ray Emission (PIXE) spectrometry for

analysis generally and for the determination of the elemental composition of rice

husks, particularly. The objective of this work is therefore to determine the elements

present in virgin rice husks using the PIXE analytical technique and to compare the

results obtained with those earlier obtained for rice husk ash using the same technique

as well as other X-ray emission analytical techniques such as X-ray Fluorescence

(XRF).

MATERIALS AND METHODS

Equipment

i. Hydraulic Press

ii. 1.7 MeV Tandem Pelletron Accelerator, model 5SDH, built by the National

Electrostatic Corporation (NEC), USA and acquired by the Centre for Energy

Research and Development (CERD), Obafemi Awolowo University, Ile-Ife,

Nigeria. The accelerator is generally used for ion beam analysis (IBA)

techniques, one of which is PIXE.

iii. End station for Ion beam analysis (IBA) designed and built by the Materials

Research Group (MRG) at Themba Labs, Sommerset West, South Africa

iv. Canberra Si(Li) PIXE detector with 30mm2 active area, Model ESLX30-150

Elemental Analysis of RHA using PIXE Technique

Sample preparation

The RHA samples were ground in a clean porcelain mortar to reduce the particle size

and ensure a uniform distribution of the particles. The ground ash samples were then

pressed into pellets using a hydraulic press before subjecting them to ion beam

analysis (IBA) using the PIXE technique.

Conversion of Concentration values from Parts per million (ppm) to Percentage

%

The PIXE concentration values of the elements generated in parts per million (ppm)

were converted to percentage (%) concentration as follows:

1 ppm = 1

1,000,000

In % = 1

1,000,000 x 100 = 1

10,000

To convert Xppm to X% = 𝑋𝑝𝑝𝑚

10,000

Elemental Analysis of Rice Husk Using Proton-Induced X-Ray Emission (Pixe).. 805

RESULTS AND DISCUSSION

The results of the elemental analysis of rice husk sample using the PIXE

spectrometric technique revealed the presence of a total of thirteen (13) elements as

shown in Table1. The PIXE spectrum for the virgin rice husks is shown in. Fig.1. The

concentration values in the PIXE spectrum are in parts per million (ppm) due to the

high sensitivity of PIXE, but were converted to percentage (%) concentration as

presented in Table 1. The predominant element was found to be Si in the form of

silica (SiO2 with a concentration of ~ 26% which is close to some literature values

[20]. This high concentration of silica in rice husks is what makes it a bio-resource of

interest to researchers. Ti and Zn were found in trace quantities, Al, Fe, Ca, Mg, Na,

K, S, Cl, Mn were present in minute quantities while P was present in a small amount

relatively. This concentration trend is in conformity with that obtained for rice husk

ash (RHA).

The total concentration value of the thirteen elements is 27.158% out of which silica

makes up 26 % and the twelve other elements make up only 1.3354%, which is

considerably low and of no commercial value like silica. This shows that silica

constitutes 95% of the total elements found present in the rice husk sample analysed.

Due to their extremely low levels, the other twelve elements are usually regarded as

impurities in rice husk ash when the husks are burnt [27]. Since the concentration of

the elements is 27.158%, it implies that the balance of 72.842% is made up of the

lignocellulosic components of rice husks, with water and extractives. These values are

in conformity with values reported in literature [18, 19].

Fig.1 PIXE Spectrum of Rice Husk

50 100 150 200 250 300 350 400

1

10

100

1000

10000

100000

GRH01_PIX_K8

Fe

MnTi

Ca

KS

Si

CO

UN

TS

CHANNEL

806 Clementina D. Igwebike-Ossi

Table 1. Elemental Components of Rice Husk using PIXE technique

Element Concentration (%) Standard Error (%)

Si as SiO2 25.82 0.024

Al 0.017 0.001

Fe 0.039 0.001

Ca 0.088 0.002

Mg 0.135 0.020

Na 0.031 0.010

K 0.099 0.003

P 0.666 0.023

S 0.217 0.009

Cl 0.026 0.005

Ti 0.006 0.001

Mn 0.012 0.001

Zn 0.001 0.000

27.158

The concentration value obtained for silicon present in the form of silica (ash) is

appreciably higher than some literature values of 15-20% [16, 18, 19] but close to

some (22-29%) [21].

Some of these thirteen elements detected in rice husks using the PIXE technique have

been reported by other X-ray emission analytical techniques such as X-ray

fluorescence (XRF). The elements reported are Fe, Ca, K, Cl, Mn and Zn [27]. The

elements not detected by PIXE but have been reported to be present using the XRF

technique are Cr, Ni, Cu, Sr, Br, I, and As [27] while those detected by PIXE but not

found using XRF are Al, Mg, Na, P,S, and Ti. This variation in the elemental

components of rice husks can be attributed to a number of factors such as rice variety,

soil chemistry, use and type of fertilizer, climatic conditions etc as earlier enumerated

[32-35]. The sensitivity and limitations of the analytical technique employed, can also

affect the elements detectable, for instance, XRF, a commonly used X-ray emission

analytical technique has some inherent design deficiencies which have reduced its

sensitivity to some elements [36].

Elemental Analysis of Rice Husk Using Proton-Induced X-Ray Emission (Pixe).. 807

Expectedly, the elements found in rice husks were also detected in rice husk ash

(except for Rb) using the PIXE technique [28]. This therefore substantiates and also

confirms the presence of these elements in rice husks. The concentration values of the

thirteen elements were lower in rice husks than in rice husk ash. This observation can

be ascribed to the presence of water and lignocellulosics in rice husks which give a

larger weight and volume of material than in the ash. When these are removed during

combustion, the reduction in weight and volume of the rice husk ash residue will give

rise to higher concentration values of these same elements in the ash. For instance, Fe,

Ca and Mg have concentration values (in %) of 0.039, 0.088 and 0.135 respectively in

rice husks, but 0.116, 0.136 and 0.543, respectively in rice husk ash [28], showing a

considerable increase in value due to the smaller volume of rice husk ash.

This explanation is also applicable to the concentration of silica in both rice husks and

rice husk ash, which values are 25.82% and 74-81% [28], respectively. The level of

silica is again higher in the ash than in the husk because when rice husk is burnt, the

water, lignocellulosics and volatiles in the husk escape leaving a smaller weight and

volume of residue, which has the same silica content (and small amounts of metallic

oxides). This is attributable to the fact that silica does not decompose readily during

burning due to its high melting point of 14400C [33], thus it is the major component

of the residue from the combustion process, which is referred to as ‘ash’ while the

other metallic oxides are often referred to as impurities due to their small

concentrations[27]. In furtherance of this phenomenon, it has been established that

virgin rice husks contain about 15-20% of ash which is largely silica [16, 18-19].

Research findings [37] have shown that when rice husk is incinerated, the ash yield is

19-24%. Thus, 15-20% of silica in 19-24% of ash will give higher silica concentration

values in rice husk ash of 79-83%, theoretically. This is close to actual values of silica

found to be present in rice husk ash samples which were in the range of 68-91%

depending on combustion temperature and duration [38].

CONCLUSION

A total of thirteen (13) elements were detected in virgin rice husks by the PIXE

analytical technique with silicon (present in the form of silica) as the predominant

element having the highest concentration value of ~26%. The other twelve elements

made up 1.3354% out of a total concentration of 27.158 %. This evidently shows

that silica constituted about 95% of the elements found present in the rice husk sample

analysed while the twelve other elements made up only 5%. Some of the twelve other

elements were in minute quantities while some were in trace quantities. The presence

of these same elements (except Rb) in rice husk ash as earlier reported substantiates

their presence in rice husks. However, the concentration values of the elements in rice

husks were found to be lower than those of rice husk ash due to the larger volume of

808 Clementina D. Igwebike-Ossi

material. The presence of six elements- Fe, Ca, K, Cl Mn and Zn in rice husks has

been reported using the XRF technique.

ACKNOWLEDGEMENT

The author is immensely grateful to Prof. E.I Obiajunwa of the Centre for Energy

Research and Development (CERD), Obafemi Awolowo University (OAU), Ile-Ife,

Nigeria for carrying out the analysis of rice husk using PIXE spectrometric technique.

REFERENCES

[1] Patel, S.A., Onkarappa, R and Shobha, K.S., 2007, “Fungal Pretreatment

Studies on Rice Husk and Bagasse for Ethanol Production”, Electronic

Journal of Environmental, Agricultural and Food Chemistry (EJEAFChe), (6)

4. pp.1921-1926.

[2] Chiang, K., Chou P., Hua, C., Chien, K and Cheeseman, C., 2009.

“Lightweight Bricks Manufacture from Water Treatment Sludge and Rice

Husks”, Journal of Hazardous Materials, vol. 171, issues 1-3, pp. 76-82.

[3] Osarenmwinda, J.O and Nwachukwu, J.C., 2007, “Effect of Particle Size on

Some Properties of Rice Husk Particleboard”, Advanced Materials Research,

vols.18-19, 43-48

[4] Hosseina, A., Hashtroudi, M.S. & Banifatemi, M., 2007 “The use of rice husks

to remove wastewater surfactants,Water and Wastewaters” Asia, July/August

2007 http://www.waterwastewaterasia.com/www_archive jul/Aug

07/52t55.pdf.

[5] http://en.wikipedia.org/wiki/rice_husk

[6] http://en.wikipedia.org/wiki/heating_valu

[7] http://www.thejakartapost.com/news/2009/01/28/rice-husk-waste-turned-

cheap-energy-cooking.htm

[8] Igwebike-Ossi, C.D., 2012, “Rice Husk Ash as New Extender in Textured

Paint” J. of Chem Soc of Nig, vol. 37, no.1 pp. 72-75

[9] Igwebike-Ossi, C.D., 2012,” Rice Husk Ash as New Flatting Extender in Red

Oxide Primer” J. of Chem Soc of Nig, vol. 37, no.2, pp. 59-64

[10] Igwebike-Ossi, C.D., 2014, “Rice Husk Ash as Flatting Extender in Cellulose

Matt Paint” American Journal of Applied Chemistry, vol.2, no.6, pp.122-127

[11] Ohoke, F.O and Igwebike-Ossi, C.D., 2015. “Formulation and Performance

Evaluation of Wood Adhesives Produced with Rice Husk Ash as New Filler”,

Elemental Analysis of Rice Husk Using Proton-Induced X-Ray Emission (Pixe).. 809

American Journal of Applied Chemistry,vol. 3, no. 2, pp.33-39.

[12] Farooq, M. A. and Dietz, K.J., 2015, “Silicon as versatile Player in Plant and

Human Biology: Overlooked and poorly understood” Front Plant Sci, 6, p.994

[13] Hodson, M .J., White, P.J., Mead, A., Broadly, M.R, 2005,” Phylogenetic

Variation in the Silicon Composition of plants, Annal. Bot, 96, pp. 1027-1046

[14] Juliano, B.O., 1985, “Rice Husk and Rice straw”, St. Paul, MN( USA) –

American Association of Cereal Chemists pp.689 – 695.

[15] Bharadwaj, A., Wang, Y., Sridhar, S., and Arunachobam, 2004, “Pyrolysis of

Rice Husk” Current Science, vol. 87, no. 7, pp.981-986

http://www.ias.ac.in/currsci/oct10.2004/98/pdf

[16] Muntohar, A.S., 2002, “Utilization of uncontrolled Burnt Rice Husk Ash in

Soil improvement”, Dimenia Teknik Sipil vol.4 no. 2 pp. 100 – 105

[17] Govindaro, V.M.H., 1980, “Utilization of Rice Husk – A Preliminary Analysis

“, J. Sci. Ind. Research, 39, pp. 495-515.

[18] Daifullah, A. A. M., Girgis, B.S., and Gad, H.M.H., 2003, “Utilization of

Agro-residues (Rice Husk) in Small Wastewater Treatment Plans”, Material

Letters, 57, pp. 1723-1731.

[19] Arnesto, L., Bahillo, A., Veijoren K., Cabanillas A. and Otero, J., 2002,

“Combination Behaviour of Rice Husk in a Bubbling Bed”, Biomass and

Bioenergy, 23, pp. 171-179

[20] Balakrishnan, S. 2006, “Rice Husk Ash Silica as a Support Material for Iron

and Ruthenium-Based Heterogeneous Catalyst”. M.Sc Thesis,School of

Chemical Sciences, Universiti Sains Malaysia.

[21] Maeda, N., Wada, I., Kawakami, M., Ueda, T and Pushpalal, G.K.D., 2001,

“Development of a New Furnace for the production of Rice Husk Ash” The

seventh CANMET/ACI International Conference on Flyash, Silica fume,

Slag and Natural Pozzolans in Concrete, Vol. 2, Chennai, July, 22-27 p.835.

[22] Subbukrishna, D.N., Suresh, K.C., Paul, P.J, Dassapa, S and Rajan, N.K..S.,

2007, “Precipitated silica fromRice Husk Ash by IPSIT process” 15th

European Biomas Conference and Exhibition, 7-11 May, Berlin,Germany.

http://cgpl.iisc.ernet.in/site/portals/0/Technologies/precipited silica.pdf.

http://www.ehow.com/about_4600805_what-silicon-dioxide.html

[23] Chockalingam, E., Sivopriya, K., Subramanian S. and Chandrasekaran 2005,

“Rice Husk Filtrate as a Nutrient medium for the growth of

Desulfotomaculum nigrificans Characterization and Sulfate Reduction

Studies” .Bioresour Technol. 96(17 ): 1880-1

810 Clementina D. Igwebike-Ossi

[24] Janvijitsakul, K. and Kuprianov ,V.I., 2006, “Polycyclic Aromatic

Hydrocarbons in Coarse Fly Ash Particles Emitted from Fluidized Bed

Combustion of Thai Rice Husk”, In Proceedings of the 2nd Joint International

Conference on Sustainable Energy and Environment (SEE), Thailand, 21-23,

November, 2006, pp. 378-383

25] Kwong, P.C.W., Wang, J.H., Chao, C., Cheung, C.W and Kendal,l G., 2004,

“Effect of Co-Combustion of Coal and Rice Husk on Combustion

Performance and Pollutant Emission” The seventh Asia-pacific International

Symposium on Combustion and Energy Utilization, Dec., 15-17, 2004, Hong

Kong, SAR

[26]. Habeeb, G.A and Fayyadh, M.M., 2009, “Rice Husk Ash Concrete: the

effect of RHA Average particle size on mechanical properties and drying

shrinkage,” Australian Journal of Basic and Applied Sciences, 3, no.3, pp.

1616-1622.

[27] Omatola, K.M and. Onojah, A.D., 2009, “Elemental Analysis of Rice Husk

Ash using X-ray Fluorescence Technique”,International Journal of Physical

Sciences 4 (4) pp. 189-193 http://www.academicjournals.org/IJPS.

[28] Igwebike-Ossi, C.D., 2016 “Elemental Analysis of Rice husk ash using

Proton-induced X-ray Emission (PIXE) Spectrometry”, International Journal

of Applied Chemistry, vol. 12, No.3 pp.233-242

[29] Oyawale, O.O., 2012, “Characterization of Rice Husk via Atomic Absorption

Spectrometry”, International Journal of Science and Technology”, 2, no 4 pp.

210 – 215.

[30] Johanssen, A.E Campbell, J.L and Malmqvist, K.G., 1995, “Particle-Induced

X-ray Emission Spectrometry (PIXE), Chemical Analysis – A series of

Monographs on Analytical Chemistry and its Application” , John Wiley and

Son Inc. New York , pp. 1- 17.

[31] http://www.elementalanalysis. com/service pixe.com

[32] Chandrasekar, S Satyanarayana and Raghavan, P.N., 2003, “Processing,

properties and Applications of Reactive Silica from Rice Husk – An

Overview” Journal of Materials Science, 38,p. 3159.

[33] Rice Husk Ash Market Study Confidential Report, 2003, http://

webarchives.nationalarchives.gov.uk

[34] Mehta, P.K., 1994, “Rice Husk Ash- A unique Supplementary Cementing

Material,” Advances in Concrete Technology, MSL Report, 94, CANMET,

pp. 419-444.

[35] Real, C., 1996, “Determination of Silica from rice husk ash,” J.Amer. Cerem

Elemental Analysis of Rice Husk Using Proton-Induced X-Ray Emission (Pixe).. 811

Soc.79, 18: pp. 2012-2016.

[36] Jenkins, R., 1999, “X- ray Fluorescence Spectrometry,” Wiley Interscience,

New York, pp. 5-7

[37] Igwebike-Ossi, C.D and Ibemesi, J.A., 2010, “Effects of Combustion

Temperature and Time on Ash Yields of Rice Husks”, Journal of Chemical

Society of Nigeria, vol. 35 no. 1, pp. 134-137.

[38] Igwebike-Ossi, C.D and Ibemesi, J.A., 2011, “Determination of Silica content

of Rice Husk Ash at Various Combustion Temperatures and Time using

Particle-induced X-ray Emission Spectrometric Technique”, Journal of

Chemical Society of Nigeria, vol. 36, no. 1, pp. 42-46

812 Clementina D. Igwebike-Ossi